Clock and Calendar Malfunction

Two years ago I bough an ASUS laptop. From day one, the clock and calendar jump to random dates in the past and in the future after I reboot the device. Sometimes it will jump to dates and times that are only off by a few days one way or the other, but most commonly it jumps back to a date from November 2009, which I can only assume is the date of manufacturing or something like that.

What I have tried:

syncing it with two different clocks online, but this has made no difference, it still jumps around.

Going in and internally adjusting the time and date every time it shifts (this gets old)

Past that, I am not sure what to do. Please let me know if there is anything I can clarify. Thank you!

When you 'shut down', do you switch off power to the mains? Don't if you can avoid it. My previous PC (a desktop) used to do that, if I ever removed power completely. It lasted years doing that (still going in fact, but retired) and kept the date as long as there was power to the machine. Replacing the cmos battery did not help.

When you change the date manually, do you do it in the bios, because if you don't, it cannot possibly be right at next boot. Prove it is the bios that won't keep the time, then you will know there is no answer and you have to live with it.